Because an alarming number of men really genuinely believe women enjoy this and it will lead to a reciprocal video or more.
This^
Because not enough people in their life (that they would listen to) have told them its not acceptable
and this^
Because even those who know its not acceptable don't care.
but mostly this^
As a pp remarked it's been likened to sex offenders i.e. flashers exposing their genitals in public for their own thrill and the revulsion/fear they get from their victim/intended target.
It's just degrading.
I suspect that for every, say, hundred unsolicited dick picks they send. They maybe get 1 or 2 tit or vag or female wanking photos back.
They don't care how many times they get blocked by other dating site users that they've sent, their own I assume, dick pick to. Sooner or later, they will get the tit or vag etc picture they wanted. Push push push. It's fucking depressing.
What's wrong with regular porn for these men, anyway ? There's enough of that online etc etc etc isn't there ?
Again, as a PP remarked that's models acting. I guess they can kid themselves a return fanny etc pic they got from someone OLD is real somehow. They just want someone who is desperate for attention and the joke is on them, ultimately.
Tragic, really.